Resonance control for a muffle burner

ABSTRACT

Vanes are provided in the inlet to the outer annular combustion air supply duct which are adjustable to change the direction of air flow by a magnitude of up to 10 percent in the tangential velocity component at the outlet of the outer duct. This avoids humming or whistling. The vanes are controlled in unison from a control lever outside the distribution box.

United States Patent 1191 1111 3,723,049 Juricek 1 Mar. 27, 1973 541 RESONANCE CONTROL FOR A 1,740,985 12/1929 Irish ..43l/l84 MUFFLE BURNER 3,391,981 7/1968 Voorheis fit al. ..431 1s4 x 1,870,026 8/1932 Rosencrants ..431/] 84 1 lnvemofi Edward Juricek, wmterthur, 3,612,737 10 1971 Sharan ...43l/l83 Switzerland 2,869,625 1/1959 Hogberg et al. ..43 1/1 84 [73] Assignee: Sulzer Brothers Ltd., Winterthur,

Swltzerland Primary Examiner-Carroll B. Dority, Jr. [22] Filed: May 26, 1971 Attorney-Kenyon & Kenyon Reilly Carr & Chapin Appl. No.: 146,978

Foreign Application Priority Data May 29, 1970 Switzerland ..8056/ US. Cl. "431/183, 431/184, 239/402, 239/402.5, 239/404 Int. Cl ..F23m 9/00 Field of Search ..431/354, 183, 184; 239/402, 239/402.5, 404

References Cited UNITED STATES PATENTS 2/1942 Haynes ..43l/l84 [5 7] ABSTRACT 6 Claims, 1 Drawing Figure PATENTEDHARZHEJB 3 723,049

Wen/0r.- fpzm p A. ave/car RESONANCE CONTROL FOR A MUFFLE BURNER This invention relates to a muffle burner and, more particularly, to a muffle burner having central means for supplying oil and/or gas fuel. Still more particularly, this invention relates to a resonance control for a muffle burner.

Muffle burners have been known, such as those described in U.S. patent application Ser. No. 880,683, filed Nov. 28, 1969 and now U.S. Pat. No. 3,612,737, which comprise a central meansfor supplying oil and/or gas fuel, a means surrounding the fuel supply means for supplying combustion air and having disposed therein means for imparting a swirl to the air flowing therethrough, and an adjoining refractory muffle. These swirl type muffle burners have the control means for supplying the liquid or gaseous fuel surrounded by at least two concentric annular combustion air supply ducts, each of which has a means disposed therein for imparting twist to the air flowing therethrough. The construction is such that, over the entire load range, the velocity of the air leaving the innermost of the annular ducts is greater than the velocity of the air leaving the outermost of the annular ducts and the tangential velocity component of the air discharged from the innermost of the annular duct is greater than the tangential velocity component of the air discharged from the outermost of the annular ducts.

However, it has been found that, during operation of these burners, resonance phenomena occur under certain loading conditions which may take the form of unpleasant humming or whistling.

Accordingly, it is an object of the invention to eliminate objectionable resonance phenomena in muffle burners of the above type.

It is another object of the invention to modify existing muffle burners with a simple construction to eliminate humming or whistling therein due to resonance.

It is another object of the invention to suppress resonance in a muffle burner with very little change in the total flow of air or in the distribution of the air flow between the ducts of the burner.

Briefly, the invention provides a muffle burner which includes a central fuel supply means, a combustion air supply means having at least two annular ducts surrounding the fuel supply means, and twist imparting means in each duct to cause the discharged air to have a tangential velocity component with a means for adjustably changing the direction of the air flowing to at least one of the twist imparting means. This direction changing means has been found to reduce or suppress the resonance phenomena easily and effectively with very little change in the total flow of air through the burner or in the distribution of the air flow between the ducts. Further, the direction changing means are so constructed that, in use, the maximum change of direction produced thereby is such that the change in the magnitude of the tangential velocity component at the outlet of the associated twist imparting means is less than percent.

In one embodiment which is particularly simple, the direction changing means comprises a plurality of vanes located adjacent the inlet of the outermost of the annular air ducts and distributed around the circumference of the duct, and means for adjusting the vanes relative to the duct. In addition, the meansfor adjusting the vanes is controllable from a position remote from the outermost duct such that the vanes can be-adjusted from outside the muffle burner. Also, the vanes can be connected in common so as to be adjusted in unison. I

These and other objects and advantages of the invention will become more apparent from the following detailed description and appended claims taken in conjunction with the accompanying drawing in which:

The drawing illustrates a cross-sectional view of a muffle burner constructed in accordance with the invention.

Referring to the drawing, the muffle burner 1 has a cylindrical air distribution box 2 to which a duct 3 for supplying combustion air to the burner is connected. The duct 3 is disposed with respect to the box 2 so that the air flows tangentially into the box 2 as is known, e.g. as described in the above mentioned patent. A burner lance 4 is located at the center of the distribution box 2 and is supplied with liquid and/or gaseous fuel via a pipeline 5. A muffle 18 constructed of suitable ceramic material defines a combustion chamber of the burner l at the outlet of the lance 4. In addition, the burner lance 4 is surrounded by two tubular members 9, 10 each of which flares out in trumpet fashion at the left hand end, as viewed in the drawing. An outer annular duct 40 is formed between the tubular members 9, l0 and an inner annular duct 50 is formed between the burner lance 4 and the inner tubular member 9. Also, a swirl means 11, 12 is positioned respectively in each of the annular .ducts 40,.50 for imparting twist to the air for combustion flowing through the ducts 40, 50. The intensity of the swirl in the annular duct 40 differs from that in the annular duct 50, but the directions of the swirls at the outlets from the two ducts are the same. The swirl means ll, 12 as in the above mentioned patent are so constructed that the tangential velocity component of the air discharged from the inner annular duct 50 is greater than the tangential velocity component of the air discharged from the outer annular duct 40, while the velocity of the air leaving the inner annular duct 50 is greater than the velocity of the air leaving the outer annular duct 40.

In order to control the total rate of flow of air for combustion, a sleeve 15 is axially displaceably mounted on the trumpet-shaped end of the tubular member 10. This sleeve 15 allows a greater or lesser air flow through the annular duct 40, depending upon the position thereof. The sliding movement of the sleeve 15 is produced by a linkage 116 which is controlled from outside the air distribution box 2, for example, by a means as described in U.S. patent application Ser. No. 89,563 filed Nov. 16, 1970 now US. Pat. No. 3,649,155.

A means for controlling the resonance of the burner 1 includes a plurality of vanes 162, e.g. six, which are mounted between the trumpet-flared ends of the tubular members 9, 10 and are distributed uniformly around the periphery of the members 9, 10. Each vane 162 is attached to a spindle 161 which is pivotally mounted in a suitable manner in the flared ends of the tubular members 9, 10 and in the end wall 163 of the air distribution box 2. Each spindle 161 carries a lever 164 adjacent the inside surface of the end wall 163, the free end of which is pivotally connected to a ring 165 so that the levers 1 64 are coupled in parallel relationship to one another. The top spindle 161, as viewed in the drawing, extends through the end wall 163 and carries a lever 166 on the outer end. The free end 167 of this lever 166 bears resiliently against the outer surface of the end wall 163 while the surface of the end wall 163 is formed with a number of radially disposed notches (not shown) in the pivoting range of the lever 166 so that the end 167 thereof can engage the notches successively. Thus, all the vanes 162 are displaced in the same direction and by the same amount by pivoting the lever 166 about the axis of the respective spindle 161.

When the burner is in operation, the total rate of flow to the burner and the distribution of the air flow through the two annular ducts 40, 50 is adjusted in dependence on the load by axial displacement of the sleeve 15. If any humming or whistling of the burner then occurs, the position of the vanes 162 is altered by actuation of the lever 166 so that the direction of the air entering the outer annular duct 40 is changed. This will produce very little change in the total flow of air to the burner l or in the distribution of the air between the two annular ducts 40, 50, but the resonance phenomena which produce humming or whistling can be eliminated by this small change of direction. The construction is such that the maximum change in direction that can be produced by the vanes 162, compared with the direction in which flow would occur if the vanes 162 were absent, is such that the change in the magnitude of the tangential velocity component at the outlet of the swirl means 11 is less than percent.

It is noted that if the optimum positions of the lever 166 for different loads have already been determined, the spindle 161 can be adjusted directly from a load controller (not shown), for example, by appropriately constructed cam discs.

Alternatively, instead of using vanes 162 to adjust the direction of air flow to only one of the two twist-imparting means, an adjustable grid or cascade (not shown) can be provided at the entrance of the duct 3 into the air distribution box 2 so that the direction of air flow for combustion to the two annular ducts can be changed simultaneously.

It is also possible to provide a vibration-measuring probe in the distribution box 2 which is capable of producing a signal corresponding to a measured vibration so that the signal produced by the probe can be used to adjust the means controlling the direction of air flow to one or to both annular ducts via an automatic control unit.

What is claimed is:

1. In combination with a muffle burner having a central means for supplying fuel, means for supplying combustion air including at least two annular ducts surrounding said central means, means in each duct for imparting twist to the air flowing through each said duct to cause the air discharged from said ducts to have a tangential velocity component; direction changing means for adjustably changing the direction of the air flowing to at least one of said twist imparting, and damper means upstream of said direction changing means for controlling the flow of air to the duct associated with said direction changing means while not obstructing the flow of air to the other of said ducts means.

2. The combination as set forth in claim 1 wherein said direction changing means is arranged to change the direction of air flowing to at least one of said twist imparting means relative to the direction of air flowing to the remainder of said twist imparting means.

3. The combination as set forth in claim 2 wherein said direction changing means includes a plurality of circumferentially distributed vanes adjacent an inlet of the outermost of said annular ducts and means for adjustin g said vanes relative to said outermost duct.

4. The combination as set forth in claim 3 wherein said means for adjusting said vanes includes a spindle connected to each vane to pivot said respective vane in said inlet, a ring connected in common to each said spindle to rotate said spindles in unison and a control lever connected to one of said spindles at a position remote from said outermost duct to rotate said one spindle to adjust said vane thereon relative to said outermost duct.

5. The combination as set forth in claim 1 wherein said direction changing means is adjustably mounted to effect a maximum change in the magnitude of the tangential velocity component at an outlet of said one twist imparting means of less than 10 percent.

6. The combustion as set forth in claim 1 wherein said damper means is a sleeve axially displaceably mounted over said ducts. 

1. In combination with a muffle burner having a central means for supplying fuel, means for supplying combustion air including at least two annular ducts surrounding said central means, means in each duct for imparting twist to the air flowing through each said duct to cause the air discharged from said ducts to have a tangential velocity component; direction changing means for adjustably changing the direction of the air flowing to at least one of said twist imparting, and damper means upstream of said direction changing means for controlling the flow of air to the duct associated with said direction changing means while not obstructing the flow of air to the other of said ducts means.
 2. The combination as set forth in claim 1 wherein said direction changing means is arranged to change the direction of air flowing to at least one of said twist imparting means relative to the direction of air flowing to the remainder of said twist imparting means.
 3. The combination as set forth in claim 2 wherein said direction changing means includes a plurality of circumferentially distributed vanes adjacent an inlet of the outermost of said annular ducts and means for adjusting said vanes relative to said outermost duct.
 4. The combination as set forth in claim 3 wherein said means for adjusting said vanes includes a spindle connected to each vane to pivot said respective vane in said inlet, a ring connected in common to each said spindle to rotate said spindles in unison and a control lever connected to one of said spindles at a position remote from said outermost duct to rotate said one spindle to adjust said vane thereon relative to said oUtermost duct.
 5. The combination as set forth in claim 1 wherein said direction changing means is adjustably mounted to effect a maximum change in the magnitude of the tangential velocity component at an outlet of said one twist imparting means of less than 10 percent.
 6. The combustion as set forth in claim 1 wherein said damper means is a sleeve axially displaceably mounted over said ducts. 